Storage photoelectric device



Sept. 7, 1937. DUDDING 2,092,206

STORAGE PHOTOELECTRIC DEVICE Filed Feb. 14, 1936 Patented Sept. 7, 1937 PATENT ()FFICE STORAGE PHOTOELECTRIC DEVICE Bernard Phineas Budding, Oxhey, England, assignor to The General Electric Company Limited, London, England Application February 14, 1936, Serial No. 63,834 In Great Britain February 22, 1935 4 Claims.

This invention relates to storage photo-electric devices, more particularly for transmitting television. By a storage device we mean one of the known kind in which a photo-electric cathode, usually consisting of a mosaic of a very large number of very small elements insulated from each other, forms one plate (or one set of plates) of a condenser (or of a set of condensers) insulated from all material conductors, the other plate (or plates) being separated from the oathode by a thin layer of dielectric and adapted to be connected conductively or inductively to an electric circuit arrangement. In the operation of such a device light is thrown on the photoelectric cathode, which thereby becomes positively charged relatively to the other plate of the condenser; after the light has acted for a predetermined time, the charge thus stored is discharged through the electric circuit, for example by means of a cathode ray incident on the cathode.

The feature of such devices with which this invention is concerned is the thin layer of dielectric; the object of the invention is to provide an improved form of thin layer. Hitherto it has usually been mica, and has therefore been entirely separate from the wall of the device. This separation involves certain inconveniences in construction, which it is the primary object of the invention to overcome.

According to the invention the said thin layer is part of the wall of an evacuated envelope, bears on its inner surface the mosaic photoelectric cathode, and is in direct contact with a metal member or members outside the envelope and forming the other plate (or plates) of the condenser. Preferably the layer is so thin that it would collapse under atmospheric pressure, if it were unsupported, and the contact between the layer and the external metal member is so intimate that the latter supports the former against collapse. The thin layer of dielectric is to be regarded as part of the wall of the envelope so long as it is not separated by a space from said wall.

One embodiment of the invention is shown by way of example in the accompanying drawing. Here the metal member I is a cup or dish of a metal or alloy having substantially the same expansion coefficient as common glasses. Thus it may be the usual nickel-iron alloy. The cup is coated internally with a thin layer of glass 2, for example, by blowing a bulb of glass against the surface. A few small holes 3 may have to be bored in the cup to allow air to escape as the bulb approaches it; they will be sealed when the layer has been formed. By this means it is possible to form on the cup a uniform layer of glass not more than 0.02 mm. thick. The edge 5 of the cup can then be sealed to a glass vessel 4 forming the greater part of the envelope. The remainder of the envelope is formed by the thin layer 2, and (as shown) this layer does not extend to the edge of the cup by the part of the cup between its edge 5 and the boundary of the thin layer. Of course this part of the cup must be continuous and not pierced with holes.

Layers much thicker than 0.02 mm. can be formed by the same process; but in general (as is well known) it is desirable to make the layer 15 as thin as possible, so that the capacity of the condenser is as large as possible. However if much thicker layers are permissible (say 0.3 mm.) an alternative method according to the invention becomes possible. A bulb is blown with an end of 20 about this thickness, and this end is coated externally with a closely adherent layer of metal. Methods of depositing thick adherent coatings of metal on glass are well known. If this thin end is too thin to support atmospheric pressure 25 unaided, the metal layer will support it.

It is sometimes desirable that the non-photoelectric plate of the cathode should be divided into several parts, which can be connected to separate circuits, so that in effect the equivalent 30 of several separate mosaic photo-tubes are formed. In the second method of manufacture proposed above this can be achieved easily by cutting lanes in the metal coating, separating electrically the parts on either side of a lane. 35 It might even be achieved in the first method. The cup would then have to consist of several parts, separated by small gaps, but held together during the internal coating with the glass layer; the gaps would provide holes through which air 40 could escape. The means holding the parts together might be removed after the glass layer is formed, and the parts left connected only by the layer; but if the layer were very thin, they would have to be retained and would then have 5 to be of insulating material.

The production of a mosaic photo-electric cathode 6 on the surface of the glass layer formed in either of these ways follows known methods, and is not part of the invention.

If a flat cathode is desired, the cup shown in the drawing could be replaced by a cylinder with a flat end; the layer could be formed on the flat end and the sides used only for making the junction with the glass envelope. But it may be ob- 55 served that a perfectly flat cathode is not always desirable; a cathode curved, as is the end of a cathode ray tube, may be preferable. For, if the curvature of the surface on which the original image is projected is the same as that of the surface on which the final image is reproduced, distortion due to curvature of these surfaces will be eliminated.

A ring anode of known kind is shown at I provided with a leading-in-wire 8.

I claim:-

1. A storage photo-electric device comprising an envelope, a part of the wall of which is in the form of a, thin layer of dielectric, a mosaic photoelectric cathode on the inner surface of said thin layer, a metal member in direct contact with the outer surface of said layer, said cathode and said metal member forming the two plates of a condenser, and an anode within the envelope.

2. A storage photo-electric device comprising an envelope, said envelope having a part made of metal, a thin coating of dielectric on the inner surface of said metal part, a mosaic photo-electric cathode on said coating, and an anode within said envelope. 7

3. A storage photo-electric device comprising an envelope containing electrodes, a thin layer of dielectric, said layer forming part of said envelope, a mosaic photo-electric cathode on the inner surface of the said layer, and a. metal member in direct contact with the outer surface of said layer, said cathode and said metal member forming the two plates of a condenser.

4. In the manufacture of a storage photo-electric device having a mosaic photo-electric cathode and a metal cup separated from the cathode by a thin layer of dielectric to form a condenser, the steps which comprise providing holes in said metal cup, blowing a bulb of glass against the inner surface of said cup to form the thin layer of dielectric on said surface, the imprisoned air escaping through said holes, sealing said holes, and forming the mosaic photo-electric cathode on said layer.

BERNARD PHINEAS DUDDING. 

